This invention relates to high contrast photographic silver halide materials containing a combination of hydrazide nucleating agents and in particular to those materials of the graphic arts type.
In the field of graphic arts, an ultrahigh contrast photographic material is required for achieving satisfactory halftone dot reproduction of a continuous tone or reproduction of a line image in the process of making a lithographic printing plate. For many years these ultrahigh contrast photographic images were obtained by developing a xe2x80x98lithxe2x80x99 emulsion (usually high in silver chloride content) in a hydroquinone, low sulphite, xe2x80x98lithxe2x80x99 developer by the process known as infectious development. However, such low sulphite developers are inherently unstable and are particularly inappropriate for machine processing.
More recently an image formation system providing ultrahigh contrast where the gamma (contrast) exceeds 10 has been provided conventionally in a material wherein silver halide bearing a surface latent image is developed in the presence of a hydrazine (also known as a nucleating agent), specifically an acylhydrazine, which can be incorporated into the photographic material or into the developer. The pH of the developer solution is usually in the range 10.0 to 12.3, typically about 11.5, and the developer includes conventional amounts of sulphite, hydroquinone and possibly metol or a pyrazolidone. While such a process is better than the low sulphite xe2x80x98lithxe2x80x99 process, the developer still has a high pH requirement for it to function correctly. Such a solution is not as stable as is desirable. Additionally, high pH solutions are environmentally undesirable because of the care needed in handling and disposing of the effluent.
Unfortunately, light sensitive materials whose contrast is enhanced by the presence of a hydrazine nucleating agent show large variations in their photographic properties as the developer is exhausted or through the course of time, for example as the pH of the developer varies and in particular as the pH is lowered. The pH of the developer can vary for a number of reasons: for example, exhaustion and absorption of carbon dioxide causes the pH to drop whilst air oxidation causes the pH to rise, as can concentration through evaporation.
Also during development of silver halide materials, particularly those which use chlorobromide emulsions, there is a release of bromide locally into area of the development as a consequence of the development process to convert silver halide to elemental silver. Both of these effects can influence the development rate of the film and give rise to process unevenness or variability during the processing run. There is an overall effect that shows up as a change to the developer component levels in solution but there is also a local effect that occurs within the developing layer and is exposure dependent. These effects can also depend on the formulation of the developer used and overcoming these problems can increase tolerance to a wider range of developer formulations.
It is also known that a developer solution having a pH below 11 can be employed by using certain hydrazides active at this pH. Hydrazides proposed for such use are described, for example, in U.S. Pat. Nos. 4,278,748; 4,031,127; 4,030,925,4,323,643, 4,988,604 and 4,994,365 and in EP-A-0 333435. A nucleator containing both a hydrazide moiety and a nicotinamide moiety is disclosed in U.S. Pat. No. 5,288,590. However the use of these nucleating agents does not entirely remove sensitivity to both bromide and pH.
A nucleating agent which comprises a dimeric molecule comprising two monomers linked by a linking group, each monomer of which (a) may be the same or different and (b) comprises a hydrazide and a nicotinamide moiety has been disclosed in EP-A-1 008 902. A nucleating agent comprising (a) two nicotinamide moieties, which may be the same or different, which are linked by a linking group, and (b) a hydrazide moiety linked to only one of those nicotinamide moieties, either alone or together with the nucleating agent comprising the dimeric molecule, has been described in EP Patent application No. 01201989.9. U.S. Pat. Nos. 4,988,604 and 4,994,365 describe aryl sulfonamidophenyl hydrazide nucleating agents that are capable of high contrast development.
Developer solutions with these low pHs can also be used by the introduction of a contrast-promoting agent (commonly called a booster) to give adequate activity. The booster can be incorporated into the photographic layer or may be dissolved in the developer solution. The booster may be, for example, one of the boosters as described in U.S. Pat. No. 5,316,889 or an amine booster as described in U.S. Pat. Nos. 4,269,929; 4,668,605, 4,740,452, 4,975,354 or EP-A-0 364166. Compounds bearing different functionalities e.g. phosphonium and pyridinium, have also been shown to be active, as described in U.S. Pat. No. 5,744,279.
The design of nucleators and boosters is continuing to develop by varying their structures to fine tune the performance of the system and to enhance image quality and process stability during the running of a process. U.S. Pat. No. 5,328,801 describes the use of an inhibitor releasing redox compound suitable for nucleated systems. The problems associated with processing unevenness are described in U.S. Pat. No. 5,882,841.
The problem is therefore to provide nucleators for incorporation into a photographic material which has improved processing evenness through a reduced sensitivity to variations in the developer pH and bromide level which occur in the film during development and which exhibits greater tolerance to a wider range of developers.
It has been found that these objectives can be achieved by the use of a combination of nucleating agent(s) of formulae (I) and/or (II) with a nucleating agent of formula (III), in which the nucleating agent of formula (I) comprises (a) two nicotinamide moieties, which may be the same or different, which are linked by a linking group, and (b) a hydrazide moiety linked to only one of those nicotinamide moieties; the nucleating agent of formula (II) comprises a dimeric molecule comprising two monomers linked by a linking group, each monomer of which (a) may be the same or different and (b) comprises a hydrazide moiety and a nicotinamide moiety; and the nucleating agent of formula (III) comprises an aryl sulfonamido aryl hydrazide.
Such a combination of nucleating agents can lead to high contrast nucleation providing excellent processing evenness in a developer whose pH is variable and can give greater tolerance to a wide range of developer solutions.
According to the present invention therefore there is provided an ultrahigh contrast photographic material comprising a support bearing a silver halide emulsion layer, containing a combination of two or more hydrazide nucleating agents in the emulsion layer and/or a hydrophilic colloid layer, characterised in that the combination comprises a nucleating agent(s) of formulae (I) and/or (II) with a nucleator of formula (III), in which the nucleating agent of formula (J) comprises (a) two nicotinamide moieties, which may be the same or different, which are linked by a linking group, and (b) a hydrazide moiety linked to only one of those nicotinamide moieties; the nucleating agent of formula (II) comprises a dimeric molecule comprising two monomers linked by a linking group, each monomer of which (a) may be the same or different and (b) comprises a hydrazide moiety and a nicotinamide moiety; and the nucleating agent of formula (III) comprises an aryl sulfonamido aryl hydrazide.
In another aspect of the invention there is provided an ultrahigh contrast photographic material, as hereinbefore defined, which also contains in the emulsion layer or a hydrophilic colloid layer, a booster compound, as hereinafter defined.
In yet another aspect of the invention there is provided a process of forming a photographic image having ultrahigh contrast which comprises imagewise exposing a photographic material comprising a support bearing a silver halide emulsion layer and processing it with an alkaline developer solution, characterised in that it is developed in the presence of a combination of two or more hydrazide nucleating agents, comprising a nucleating agent of formula (I) and/or (II) with a nucleating agent of formula (III), optionally in the presence of a booster compound, as hereinafter defined.
The combination of nucleating agents for use in the invention show less sensitivity to variation in the development conditions than do the individual nucleating types.
This leads to significant improvements in processing robustness with reduced density variation across the length and width of processed sheets, making the processing more uniform and reducing the variation in the day-to-day running of the film and processor. There is less change in image quality with processing and tolerance to a wider range of developer solutions.
The nucleators of formula (I) for use in photographic materials of the invention preferably have one of the following general formulae: 
wherein BG is a blocking group;
one of A1 and A2 is a hydrogen atom and the other is a hydrogen atom, an acyl group or an alkyl- or aryl-sulfonyl group, any of which groups may be substituted,
Z1 and Z2 are the same or different and each is a nicotinamide residue, at least one of which is positively charged;
Y is a substituted aryl or heterocyclic ring;
L is a linking group;
T is an anionic counterion
and n is 1 or 2.
The nucleators of formula (II) preferably have one of the following general formulae: 
wherein each monomer linked by linking group L is the same or different;
Z is a positively charged nicotinamide residue; and
Y, A1, A2, BG, L and T are as defined for a compound of formula (I).
The nucleators of formula (III) preferably have the general formula: 
wherein V and W are independently a substituted or unsubstituted arylene group;
r is 1 to 6;
R is selected from the class consisting of Sxe2x80x94Rxe2x80x2, wherein Rxe2x80x2 is an unsubstituted or substituted monovalent group comprising at least three ethyleneoxy units, and a positively charged pyridinium residue substituted with from 1 to 3 unsubstituted or substituted alkyl groups, with its associated cation;
and A1, A2 and BG are as defined for a compound of formula (I).
In a preferred embodiment in each of the formulae (I), (II) and (III) d A2 is a hydrogen atom.
More preferably the nucleating agent of formula (I) has one of the following formulae A, B or C, formula A being the most preferred: 
More preferably the nucleating agent of formula (II) has one of the following formulae D, E or F, formula D being the most preferred: 
More preferably the nucleating agent of formula (III) has one of the following formulae (G) or (H): 
In these embodiments (A) to (H),
each R1CO comprises a blocking group and in particular each R1 is independently selected from a hydrogen atom and an unsubstituted or substituted alkyl, aryl, alkoxy, aryloxy, alkoxy- or aryloxy-carbonyl and alkyl- or aryl-aminocarbonyl group; or each R1 independently is or contains an unsubstituted or substituted heterocyclic group, having a 5- or 6-membered ring containing at least one nitrogen, oxygen or sulfur atom, wherein the ring may be linked either directly to the carbonyl group or via an alkyl, alkoxy, carbonyl, amino- or alkylamino-carbonyl group and wherein the ring may be fused to a benzene ring;
each R2 and each R3 is independently selected from hydrogen and an unsubstituted or substituted alkyl or aryl group and each p is independently 0 or 1;
each R4 and each R5 and each R6 is independently selected from hydrogen, halogen, hydroxy, cyano and an unsubstituted or substituted alkyl, aryl, heterocyclyl, alkoxy, acyloxy, aryloxy, carbonamido, sulfonamido, ureido, thioureido, semicarbazido, thiosemicarbazido, urethane, quaternary ammonium, alkyl- or aryl-thio, alkyl- or aryl-sulfonyl, alkyl- or aryl-sulfinyl, carboxyl, alkoxy- or aryloxy-carbonyl, carbamoyl, sulfamoyl, phosphonamido, diacylamino, imido or acylurea group, a group containing a selenium or a tellurium atom, and a group having a tertiary sulfonium structure;
each m is independently an integer from 0 to 4;
each q is independently an integer from 0 to 4;
each R7 is independently selected from hydrogen and an unsubstituted or substituted alkyl or aryl group;
each X is independently selected from C, Sxe2x95x90O and Cxe2x80x94NH;
each (link1) is a linking group independently selected from an unsubstituted or substituted alkylene, polyalkylene, aryl, arylaminocarbonyl or heterocyclyl group and each n is independently 0 or 1;
each (link2) is a linking group independently selected from an unsubstituted or substituted polyalkylene, polyalkylene oxide, polyalkylene containing one or more heteroatoms selected from nitrogen, oxygen and sulfur, separated from each other by alkylene groups, or an unsubstituted or substituted polyalkylene in which the alkylene groups are separated by an unsubstituted or substituted aryl or heterocyclic ring;
V is an unsubstituted or substituted phenylene or naphthalene group;
Rxe2x80x2 is an unsubstituted or substituted monovalent group comprising at least three ethyleneoxy units;
Rxe2x80x3 is an unsubstituted or substituted alkyl group;
r is 1 to 6;
s is 1 to 3
and
Txe2x88x92 is an anionic counterion.
The term xe2x80x98blocking groupxe2x80x99 refers to a group suitable for protecting the (hydrazine) group but which is readily removable when necessary.
It is preferred that R1 is a hydrogen atom or a group selected from unsubstituted or substituted alkyl, for example methyl, trifluoromethyl, 3-methylsulfonamidopropyl, methyl- or phenyl-sulfonylmethyl, carboxy-tetrafluoroethyl; unsubstituted or substituted aryl, for example phenyl, 3,5-di-chlorophenyl, o-methane-sulfonamidophenyl, 4-methanesulfonylphenyl, 2(2xe2x80x2-hydroxyethyl)phenyl, 2-hydroxy-4-methylphenyl, 2-hydroxymethylphenyl, o-hydroxybenzyl, hydroxyalkylbenzyl; a carbonyl-containing group, for example an alkylamino-, alkoxy-, aryloxy- or hydroxyalkylamino-carbonyl; or contains an imidazolyl, pyrazolyl, triazolyl, tetrazolyl, pyridyl, pyridinium, piperidinyl, morpholino, quinolinium or a quinolinyl group or R1 may include a group which splits off a photographically useful fragment, such as a phenylmercaptotetrazole or a 5-or 6-nitroindazole group. Examples of some of these are disclosed in U.S. Pat. No. 5,328,801.
More preferably in compounds of formulae (I) and (II) R1 contains a morpholino group and especially has the formula xe2x80x94CONH(CH2)n-morpholino, wherein n is 0-4 and is conveniently 3.
R2 and R3 are preferably hydrogen atoms or alkyl groups with p being preferably 1 and R4, R5 and R6 being preferably hydrogen, alkyl, alkoxy, alkylthio, trifluoromethyl or methylsulfonamido groups, with q being preferably 0 or 1 and m being preferably 0. R7 is preferably hydrogen or an alkyl group, optionally substituted with, for example, a dialkylamino group.
When X is Sxe2x95x90O or Cxe2x80x94NH it is preferred that n is 1 and that (link,) comprises an arylamino group or an arylaminocarbonyl group, preferably a phenylaminocarbonyl group, which may be substituted in the ring, for example, with one or more alkyl, carboxyl groups or halogen atoms. When X is C it is preferred that n is 0 such that no (link1) group is present.
The (link2) group preferably comprises a polyalkylene group comprising alkylene groups, preferably methylene groups, typically four or six, which may be separated by one or more O or S atoms. For example (link2) may be (CH2)4, (CH2)6, (CH2)2S(CH2)2 or (CH2)2O(CH2)2O(CH2)2. Alternatively (link2) may be a polyalkylene oxide chain extending from an even number of methylene groups such as (CH2CH2O)14CH2CH2 or may comprise, for example, a CHU2C6H4CH2 group.
In formula (III), both V and W may be substituted with one or more substituents such as, or example, an alkyl, halo, alkoxy, haloalkyl or alkoxyalkyl group. V and W are preferably each a phenylene group.
In formula (G) there are least three repeating ethyleneoxy units in Rxe2x80x2, more preferably from four to fourteen units and even up to fifty repeating ethyleneoxy units. In formula (H) the sum of the number of carbon atoms represented by Rxe2x80x3 is preferably at least 4, more preferably at least 8, each Rxe2x80x3 group preferably having from 1 to 12 carbon atoms.
The anionic counterion may be selected from any well known in the art and may typically be selected from Clxe2x88x92, Brxe2x88x92, Ixe2x88x92, CF3COOxe2x88x92, CH3SO3xe2x88x92 and TsOxe2x88x92.
As used herein and throughout the specification the term alkyl refers to an unsaturated or saturated straight or branched chain alkyl group (including alkenyl and aralkyl) having 1-20 atoms and includes cycloalkyl having 3-8 carbon atoms. The term aryl specifically includes fused aryl and the term heterocyclic specifically includes fused heterocyclic within its scope. The term polyalkylene is defined as the group (CH2)n wherein n is an integer from 2 to 50.
Unless otherwise specifically stated, substituent groups usable on molecules herein include any groups, whether substituted or unsubstituted, which do not destroy properties necessary for photographic utility.
When the term xe2x80x9cgroupxe2x80x9d is applied to the identification of a substituent containing a substitutable hydrogen, it is intended to encompass not only the substituent""s unsubstituted form, but also its form further substituted with any group or groups as herein mentioned.
Suitably, the group may be halogen or may be bonded to the remainder of the molecule by an atom of carbon, silicon, oxygen, nitrogen, phosphorus, or sulfur. The substituent may be, for example, halogen, such as chlorine, bromine or fluorine; nitro hydroxyl; cyano; carboxyl; or groups which may be further substituted, such as alkyl, including straight or branched chain alkyl, such as methyl, trifluoromethyl, ethyl, t-butyl, 3-(2,4-di-t-pentylphenoxy) propyl, and tetradecyl; alkenyl, such as ethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy, 2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy, tetradecyloxy, 2-(2,4-di-t-pentylphenoxy)ethoxy, and 2-dodecyloxyethoxy; aryl such as phenyl, 4-t-butylphenyl, 2,4,6-trimethyl-phenyl, naphthyl; aryloxy, such as phenoxy, 2-methylphenoxy, alpha- or beta-naphthyloxy, and 4-tolyloxy; carbonamido, such as acetamido, benzamido, butyramido, tetradecanamido, alpha-(2,4-di-t-pentylphenoxy)-acetamido, alpha-(2,4-di-t-pentylphenoxy)butyramido, alpha-(3-pentadecylphenoxy)-hexanamido, alpha-(4-hydroxy-3-t-butylphenoxytetradecanamido, 2-oxo-pyirolidin-1-yl, 2-oxo-5-tetradecylpyrrolidin-1-yl, N-methyltetradecanamido, N-succinimido, N-phthalimido, 2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo-1-imidazolyl, and N-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino, benzyloxycarbonylamino, hexadecyloxycarbonylamino, 2,4-di-t-butylphenoxycarbonylamino, phenylcarbonylamino, 2,5-(di-t-pentylphenyl)carbonylamino,p-dodecyl-phenylcarbonylamino, p-toluylcarbonylamino, N-methylureido, N,N-dimethylureido, N-methyl-N-dodecylureido, N-hexadecylureido, N,N-dioctadecylureido, N,N-di-octyl-Nxe2x80x2-ethylureido, N-phenylureido, N,N-diphenylureido, N-phenyl-N-p-toluyl-ureido, N-(m-hexadecylphenyl)ureido, N,N-(2,5-di-t-pentylphenyl)-Nxe2x80x2-ethylureido, and t-butylcarbonamido; sulfonamido, such as methylsulfonamido, benzene-sulfonamido, p-toluylsulfonamido, p-dodecylbenzenesulfonamido, N-methyltetra-decylsulfonamido, N,N-di-propylsulfamoylamino, and hexadecylsulfonamido; sulfamoyl, such as N-methylsulfamoyl, N-ethylsulfamoyl, N,N-di-propylsulfamoyl, N-hexadecylsulfamoyl, N,N-dimethylsulfamoyl; N-[3-(do-decyloxy)propyl]-sulfamoyl, N-[4-(2,4-di-t-pentylphenoxybutyl]sulfamoyl, N-methyl-N-tetradecyl-sulfamoyl, and N-dodecylsulfamoyl; carbamoyl, such as N-methylcarbamoyl, N,N-dibutylcarbamoyl, N-octadecylcarbamoyl, N-[4-(2,4-di-t-pentylphenoxy)-butyl] carbamoyl, N-methyl-N-tetradecylcarbamoyl, and N,N-dioctylcarbamoyl; acyl, such as acetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl, p-dodecyloxy-phenoxycarbonyl, methoxycarbonyl, butoxycarbonyl, tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl, 3-pentadecyloxycarbonyl, and dodecyloxy-carbonyl; sulfonyl, such as methoxysulfonyl, octyloxysulfonyl, tetradecyloxy-sulfonyl, 2-ethylhexyloxysulfonyl, phenoxysulfonyl, 2,4-di-t-pentylphenoxysulfonyl, methylsulfonyl, octylsulfonyl, 2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecyl-sulfonyl, phenylsulfonyl, 4-nonylphenylsulfonyl, and p-toluylsulfonyl; sulfonyloxy, such as dodecylsulfonyloxy, and hexadecylsulfonyloxy; sulfinyl, such as methyl-sulfinyl, octylsulfinyl, 2-ethylhexylsulfinyl, dodecylsulfinyl, hexadecylsulfinyl, phenylsulfinyl, 4-nonylphenylsulfinyl, and p-toluylsulfinyl; thio, such as ethylthio, octylthio, benzylthio, tetradecylthio, 2-(2,4-di-t-pentylphenoxy)ethylthio, phenylthio, 2-butoxy-5-t-octylphenylthio, and p-tolylthio; acyloxy, such as acetyloxy, benzoyloxy, octadecanoyloxy, p-dodecylamidobenzoyloxy, N-phenylcarbamoyloxy, N-ethylcarbamoyloxy, and cyclohexylcarbonyloxy; amine, such as phenylanilino, 2-chloroanilino, diethylamine, dodecylamine; imido, such as 1 (N-phenylimido)ethyl, N-succinimido or 3-benzylhydantoinyl; phosphate, such as dimethylphosphate and ethylbutylphosphate; phosphite, such as diethyl and dihexylphosphite; a heterocyclic group, a heterocyclic oxy group or a heterocyclic thio group, each of which may be substituted and which contain a 3 to 7-membered heterocyclic ring composed of carbon atoms and at least one hetero atom selected from the group consisting of oxygen, nitrogen and sulfur, such as 2-furyl, 2-thienyl, 2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such as triethylammonium; and silyloxy, such as trimethylsilyloxy.
If desired, the substituents may themselves be further substituted one or more times with the described substituent groups. The particular substituents used may be selected by those skilled in the art to attain the desired photographic properties for a specific application and can include, for example, hydrophobic groups, solubilizing groups, blocking groups, releasing or releasable groups and groups which adsorb to silver halide. Generally, the above groups and substituents thereof may include those having up to 48 carbon atoms, typically 1 to 36 carbon atoms and usually less than 24 carbon atoms, but greater numbers are possible depending on the particular substituents selected.
In some embodiments, the nucleators of the invention may be selected from the following: 
The photographic material of the invention may also contain a booster compound to enhance the ultrahigh contrast and to promote activity. Alternatively the booster compound can be present in the developer solution.
One class of such boosters are amines which
(1) comprise at least one secondary or tertiary amino group, and
(2) have an n-octanol/water partition coefficient (log P) of at least one, preferably at least three, and most preferably at least four,
log P being defined by the formula:       log    ⁢          xe2x80x83        ⁢    P    =      log    ⁢                  [                  X          octanol                ]                    [                  X          water                ]            
wherein X is the concentration of the amino compound.
Preferably such an amine contains within its structure a group comprising at least three repeating ethyleneoxy units as described in U.S. Pat. No. 4,975,354. These units are preferably directly attached to the nitrogen atom of a tertiary amino group.
Included within the scope of the amino compounds that may be utilised in this invention are monoamines, diamines and polyamines. The amines can be aliphatic amines or they can include aromatic or heterocyclic moieties. Aliphatic, aromatic and heterocyclic groups present in the amines can be substituted or unsubstituted groups. Preferably, the amine boosters are compounds having at least 20 carbon atoms.
Preferred amino compounds for inclusion in photographic materials of the invention are bis-tertiary amines which have a partition coefficient of at least three and a structure represented by the formula:
R1R2N(CH2CH2O)nCH2CH2NR3R4 
wherein n is an integer from 3 to 50, and more preferably 10 to 50;
R1, R2, R3 and R4 are, independently, alkyl groups of 1 to 8 carbon atoms, or
R1 and R2 taken together represent the atoms necessary to complete a heterocyclic ring, and/or R3 and R4 taken together represent the atoms necessary to complete a heterocyclic ring.
A particularly preferred booster for use in photographic materials of the invention or in the developer therefor is the booster B1 wherein in the above formula R1, R2, R3 and R4 are each n-propyl groups and n is 14, i.e. the structure: 
Another preferred group of amino compounds is that of bis-secondary amines which have a partition coefficient of at least three and a structure represented by the formula:
RHN(CH2CH2O)nCH2CH2NHR 
wherein n is an integer from 3 to 50, and more preferably 10 to 50, and
each R is, independently, a linear or branched, substituted or unsubstituted, alkyl group of at least 4 carbon atoms.
Particular amines suitable as booster compounds are listed in EP-A-0 364 166.
Other types of boosters are described in U.S. Pat. No. 5,744,279 as having one of the formulae:
(a) Y((X)nxe2x80x94Axe2x80x94B)M
wherein
Y is a group which adsorbs to silver halide,
X is a divalent linking group composed of hydrogen, carbon, nitrogen and sulfur atoms,
A is a divalent linking group,
B is an amino group that may be substituted or an ammonium group of a nitrogen-containing heterocyclic group,
m is 1,2 or 3 and
n is 0 or 1,
(b) R1R2Nxe2x80x94R3xe2x80x94(X)nxe2x80x94SMx 
wherein
R1 and R2 are each hydrogen or an aliphatic group, or R1 and R2 may together form a ring,
R3 is a divalent aliphatic group,
X is a divalent heterocyclic ring having at least one nitrogen, oxygen or sulfur atom as heteroatom,
n is 0 or 1,
M is hydrogen or an alkali metal atom, alkaline earth metal atom, a quaternary ammonium, quaternary phosphonium atom or an amidino group, and
x is 1 when M is a divalent atom;
said compound optionally being in the form of an addition salt;
(c) a phosphonium structure as disclosed in col. 8 of U.S. Pat. No. 5,744,279 and as exemplified by the following formula: 
or
(d) a pyridinium structure as disclosed in col. 21 of the aforementioned US patent as exemplified by the following formula: 
The nucleators and optionally the booster compound can be incorporated in the photographic element, for example in a silver halide emulsion layer. Alternatively they can be present in a hydrophilic colloid layer of the photographic element, preferably a hydrophilic layer which is coated to be adjacent to the emulsion layer in which the effects of the nucleator are desired. They can however be present in the photographic element distributed between or among emulsion and hydrophilic colloid layers, such as undercoating layers, interlayers and overcoating layers.
The total amount of nucleating agent of formula (J) and/or (II) is from about 0.3 xcexcmol/m2 to 70 xcexcmol/m2, preferably 1 xcexcmol/m2 to 10 xcexcmol/m2, more preferably 2 xcexcmol/m2 to 7 xcexcmol/m2. The amount of nucleating agent of formula (III) is from about 0.14 xcexcmol/m2 to 70 xcexcmol/m2, preferably 0.7 xcexcmol/m2 to 14 xcexcmol/m2, more preferably 1.4 xcexcmol/m2 to 7 xcexcmol/m2. Preferably the ratio of the amount of a nucleating agent of formula (I) and/or (II): a nucleating agent of formula (III) is greater than 1.0, preferably greater than 1.5. Corresponding amounts for the booster are from 0 mol/m2 to about 1 mmol/m2, preferably 10 xcexcmol/m2 to 100 xcexcmol/m2, most preferably 30 xcexcmol/m2 to 100 xcexcmol/m2.
When a nucleating agent of formula (I) is in combination with a nucleating agent of formula (II), any relative proportions of the components may achieve the advantages of the invention. However preferably the amount of nucleating agent of formula (I): nucleating agent of formula (II) is in the range from about 10:90 to about 90:10, preferably from about 20:80 to about 80:20. Conveniently however for simplicity of synthesis the nucleating agent of formula (II) is produced in excess and generally the relative amounts of the components are then in the range about 10:90 to about 30:70.
The emulsions employed in photographic materials of the invention and the addenda added thereto, the binders, supports etc. may be as described in Research Disclosure Item 36544, September 1994, published by Kenneth Mason Publications, Emsworth, Hants, PO10 7DQ, United Kingdom, which will be identified hereinafter by the term xe2x80x9cResearch Disclosure.xe2x80x9d
The hydrophilic colloid may be gelatin or a gelatin derivative, polyvinylpyrrolidone or casein and may contain a polymer. Suitable hydrophilic colloids and vinyl polymers and copolymers are described in Section IX of the Research Disclosure. Gelatin is the preferred hydrophilic colloid.
The photographic materials may also contain an overcoat hydrophilic colloid layer which may also contain a vinyl polymer or copolymer located as the last layer of the coating (furthest from the support). It contains one or more surfactants to aid coatability and may also contain some form of matting agent. The vinyl polymer is preferably an acrylic polymer and preferably contains units derived from one or more alkyl or substituted alkyl acrylates or methacrylates, alkyl or substituted alkyl acrylamides, or acrylates or acrylamides containing a sulfonic acid group.
The photographic materials of the invention preferably contain an antihalation layer that may be on either side of the support, preferably on the opposite side of the support from the emulsion layer. In a preferred embodiment an antihalation dye is contained in the hydrophilic colloid underlayer. The dye may also be dissolved in or dispersed in the underlayer. Suitable dyes are listed in the Research Disclosure disclosed above.
The emulsions are preferably chemically sensitised, for example with both sulfur and gold. The latent-image forming grains can be bromoiodide, chlorobromoiodide, bromide, chlorobromide, chloroiodide or chloride, preferably chlorobromide. They should preferably be spectrally sensitised. More than one type of spectrally sensitised silver halide grain may be present and hence grains sensitised to different spectral regions may be present in the emulsion layer.
The coating may be made by blending two or more emulsion melts containing grains of the required spectral sensitivity, allowing the production of multi-wavelength sensitive products and giving rise to manufacturing cost advantages through both material and inventory reduction. Combining the different emulsion grains within one layer can give improvements in process sensitivity over multilayer graphics nucleated systems, as described in EP-A-0 682 288.
The silver halide grains may be doped with rhodium, ruthenium, iridium or other Group VIII metals either alone or in combination, preferably at levels in the range 10xe2x88x929 to 10xe2x88x923, preferably 10xe2x88x926 to 10xe2x88x923 mole metal per mole of silver. The grains may be mono- or poly-disperse. The preferred Group VIII metals are rhodium and/or iridium and ammonium pentachlororhodate may conveniently be used.
The present photographic materials are particularly suitable for exposure by red or infra-red laser diodes, light emitting diodes or gas lasers, e.g. a helium/neon or argon laser.
The light-sensitive silver halide contained in the photographic elements can be processed following exposure to form a visible image by associating the silver halide with an aqueous alkaline medium in the presence of a developing agent contained in the medium or the element. The photographic elements of this invention can be processed in conventional developers as opposed to specialised developers sometimes employed in conjunction with lithographic photographic elements to obtain very high contrast images. When the photographic elements contain incorporated developing agents the elements can be processed in the presence of an activator, which can be identical to the developer in composition, but otherwise lacking a developing agent.
Very high contrast images can be obtained at pH values below 11, preferably in the range of from 10.0 to 10.8, preferably in the range of 10.3 to 10.5 and especially at pH 10.4.
The developers are typically aqueous solutions, although organic solvents, such as diethylene glycol, can also be included to facilitate the solution of organic components. The developers contain one or a combination of conventional developing agents, such as, for example, a polyhydroxybenzene, such as dihydroxybenzene; aminophenol, paraphenylenediamine; ascorbic acid, eiythorbic acid and derivatives thereof, pyrazolidone, pyrazolone, pyrimidine, dithionite and hydroxylamine.
It is preferred to employ hydroquinone and 3-pyrazolidone developing agents in combination or an ascorbic acid-based system. An auxiliary developing agent exhibiting superadditive properties may also be used. The pH of the developers can be adjusted with alkali metal hydroxides and carbonates, borax and other basic salts. It is, as previously mentioned, a particular advantage of the present invention that the use of nucleators as described herein reduces the sensitivity of the photographic material to changes in this developer pH.
To reduce gelatin swelling during development, compounds such as sodium sulfate can be incorporated into the developer. Chelating and sequestering agents, such as ethylenediaminetetraacetic acid or its sodium salt, can be present. Generally any conventional developer can be used in the practice of this invention. Specific illustrative photographic developers are disclosed in the Handbook of Chemistry and Physics, 36th Edition, under the title xe2x80x9cPhotographic Formulaexe2x80x9d at page 30001 et seq. and in xe2x80x9cProcessing Chemicals and Formulasxe2x80x9d 6th Edition, published by Eastman Kodak Company (1963).
The invention will now be described with reference to the following examples that are in no way to be considered as limiting the scope thereof.